Description: (Applicant's Description) At UCSD, flow cytometers and cell sorting machines are now regarded as essential equipment to provide as a shared resource for its investigators. The cost of purchasing, servicing and staffing instruments of this degree of complexity with reliable technical expertise is viewed as beyond the realm of most individual investigators. The speed at which these automated instruments can examine or separate free floating cell populations for several parameters, sometimes simultaneously, and chart the results has provided powerful new opportunities for obtaining data on cell populations of statistically reliable size. Without access to well-maintained and serviced instruments of this type and expert assistance in their use and interpretation of the results, many experiments that can provide valuable information would be too labor intensive and prohibitively expensive. Investigators who do not have such access for appropriate work are handicapped in their opportunities to publish in reputable journals and in competitive grant applications. In combination with the other shared resources which have been created at this Center, namely Molecular Pathology, Animal Experimentation and Informatics, the enhancement of the Histology Resource and the Digital Imaging Resource composes an exceptionally versatile analytical combination. The goal of this Resource in the next funding cycle is to expand the distinguished and reliable service it has given to the Immunology, Bone Marrow Transplant team and Molecular Virology programs, to also accommodate the needs of the Cancer Genetics, Cancer Biology, Cancer Pharmacology and Translational Oncology Programs. Specific aims are to encourage and facilitate collaborations between Center Members and to coordinate the work of the Resource with that of other Center resources wherever possible to achieve enhancement of the research conducted by Members. The magnetic sorting technology opens more opportunities for sorting living cells which are minority populations within a sample and for either studying them in isolation or after modification and reinfusion back into animal hosts. We are enthusiastic about the new experimental possibilities, which will be afforded when this technology is offered on general release here soon.